1. Field of the Invention
This invention is concerned with photography and, more particularly, with the formation of multicolor photographic images.
2. Description of the Prior Art
It is well known that photographic films, and especially multicolor films, may and generally do vary sensitometrically from lot to lot, notwithstanding efforts to "repeat" previous films.
Equipment used to coat multicolor films is highly precise but variations between intended coverages of silver halide and/or the dye image-providing materials do occur. Repeat batches of silver halide emulsions may, and usually do, vary in their photographic response. Individual layers may be dried to slightly different degrees. Manufacturers of multicolor photographic films have thus developed a number of procedures to minimize the effects upon the final multicolor image of unavoidable variations in the manufacturing operations.
If the film is designed to be developed by a photofinisher or in a darkroom, processing of the exposed multicolor film may be controlled within very narrow limits in order to minimize sensitometric variations from film to film. Where the multicolor film is of the negative type, an opportunity to adjust the sensitometry occurs in printing the desired final positive image, during which operation the printing exposure may be appropriately color filtered, for example, by a "masking" technique.
Obviously the basic sources of sensitometric variations noted above also exist in multicolor diffusion transfer films, with the added complication that once the film is shipped, the sensitometric properties are essentially fixed. The opportunity for adjustment provided in darkroom processing, practically speaking, is unavailable for users of self-developing films. While professional and advanced amateur photographers may be skillful enough to utilize color correction filters to at least partially "rebalance" the color balance, ordinary users of the film would only be confused by such additional operations; more important, however, is the fact that the use of these color correction filters usually results in an undesirable reduction of the effective film speed.
Accordingly, if deviations in the intended sensitometry are discovered during the coating of the photosensitive material, for example, from tests on in-process inspection samples, immediate corrective action is very desirable in order to avoid coating a large amount of material which may not be acceptable or salvageable after the coating run has been completed. It is possible to make changes in the sensitometric characteristics of the resulting multicolor transfer image during coating by making changes in the coverages or ratios of the silver halide and/or dye image-providing materials. However, these changes in the essential image-forming components of the photosensitive element oftentimes result in quite complex and unpredictable changes in sensitometry and are likely to have an undesirable effect on sensitometric parameters other than the color balance, for example, transfer density, color saturation, processing temperature latitude, ageing and the like. Furthermore, what may be an optimum ratio of components for color balance may not also be the optimum ratio for the other sensitometric parameters.
Prior to the present invention, light absorbing substances have been put to a variety of uses in photosensitive elements including, (a) filters in overcoatings to protect the light sensitive emulsion or emulsions from the action of light which it is not desired to record, e.g., ultraviolet light absorbers; (b) filters in layers arranged between emulsions of different color sensitivity to protect them from exposure to light of the wrong color, e.g., the well known yellow filter to protect red- and gree-sensitized emulsions from the action of blue light; (c) filters in backing layers forming the so-called "antihalation" layers on either side of a transparent support carrying the light-sensitive emulsion or emulsions; (d) spectral correction filters which selectively absorb light of undesired wavelength, e.g., integral masking filters and filters employed for obtaining acceptable color rendition upon exposure to a variety of illuminants such as described in Schwan et al U.S. Pat. No. 3,672,898; and (e) "trimming" filters for reducing excess photographic speed, e.g., in the lower speed emulsion of a "doubly coated" emulsion designed to increase exposure latitude to light of a specified wavelength such as described in Wyskoff, U.S. Pat. No. 3,663,228.
More specifically, Beckett et al U.S. Pat. No. 3,547,640 disclose the incorporation of at least one nondiffusing, nonbleachable, nonimage-recording colored material in the support layer, or in one or more hydrophilic colloid layers of the photographic element through which light passes when the developed color reproduction is viewed or used to expose other color elements such as color positive materials, In Beckett, the incorporated filter material must remain with the viewed image to compensate for any image dye deficiencies in minimum density areas of the color reproduction without appreciably affecting the color balance in the other portions of the sensitometric curve. In contrast with Beckett, the filter material of the present invention is not present in the viewed image, which is formed by diffusion transfer in a distal location relative to the layer in which the filter material was introduced.
As previously indicated, filters have also been heretofore incorporated in upper layers of a photographic element through which light must pass to expose lower lightsensitive layers. For example, Higgins et al U.S. Pat. No. 2,697,036 employs such light-absorbing materials in a multilayer color photographic film to reduce light-scattering effects of turbid upper layers during exposure and then removes the filter material during processing. Land U.S. Pat. No. 2,966,408 describes the use of a nontransferable pigment e.g., a yellow dye, in the outermost layer of the photosensitive element to reduce excess photographic speed in a silver diffusion transfer process, thereby eliminating the necessity of a light filter before the camera lens.
In most processes described above, the density of any incorporated filter is set prior to coating at a specified value which is predetermined by the expected photographic properties of a particular emulsion. If unexpected variations in sensitometry are discovered during coating, the process is usually either shut down for modification of coating coverages or the deviate material is continued to be coated and salvaged later by other techniques.
The present invention is directed to correcting the unexpected sensitometric variations which may be discovered during the coating of the photosensitive element, and provides this correction without significantly interrupting the coating process or the predetermined relationships between the image-forming components.